1. Field of the Invention
The present invention is related to a vehicle anti-theft system, and particularly to a vehicle anti-theft system in which the start-up of the engine is enabled on condition that a predetermined relationship is satisfied by an ID code previously registered in the engine key or the like and another ID code previously registered in the vehicle.
2. Description of the Prior Art
In various proposals for preventing the theft of a vehicle such as a car, the vehicle is prevented from being started or it is immobilized by mechanical and/or electrical means when it is attempted to be started or moved using a wrong key. This is achieved by previously storing an identification code or a key ID code in a key, reading the key ID code when the key is inserted into a key cylinder to start the vehicle, comparing it with a reference ID code prestored in the vehicle, generating an enable signal only when there is a match between both ID codes, and enabling the engine to be started up only when an engine control unit successfully receives the enable signal. In this case, since a theft may be committed by mechanical breakage or illegal wiring if the enable signal is a binary signal of on/off, the encoding of the enable signal has been proposed, for instance, in the "Car Technology", Vol. 48, No. 8, 1994, pp. 59-64.
An example of a conventional transponder type immobilizer is shown in FIG. 8. A key 2 includes a memory (not shown) in which a key ID code (for instance, of 64 bits) is prestored, and a transmitter 4 for transmitting the key ID code. The transmitter 4 of the key 2 and a key cylinder 5 are coupled together by, for instance, an induction coil (antenna) 6.
When the key 2 is inserted into the key cylinder and rotated to the ignition ON position, an ignition switch 7 is closed. In response to this, an immobilizer CPU 13 operates, and operating electric power is supplied from a power amplifier of an antenna unit 29 to the transmitter 4 through the coil (antenna) 6. The transmitter 4 responds to this to read the key ID code, and transmits it to the key cylinder 5.
The received key ID code is amplified in the antenna unit 29, digitized by an I/F circuit 12 in the immobilizer 10, and read into the CPU 13 and temporarily stored in an appropriate ID code register 13B in the CPU 13. In an EEPROM 13A of the CPU 13, a unique reference ID code assigned to each vehicle is prestored, and the reference ID code and the key ID code which was read in are compared with each other by a compare unit 13S of the CPU 13. If it is determined that there is a match between the two codes or they are in a predetermined relationship, an enable signal is transmitted from the compare unit 13S to an engine control unit (engine ECU) 16. At the same time, a starter relay is activated to initiate the rotation of a starter motor (not shown).
In a ROM 15 of the engine ECU 16, an engine control program is stored which includes at least an engine control algorithm 15a, an I/O (Input/Output) control algorithm 15b and an anti-theft algorithm 15c. The engine ECU 16 operates according to the engine control program, and discriminates or verifies the reception of an enable code by the anti-theft algorithm 15c. If the enable signal is correct data, the engine ECU 16 performs a specific control based on the engine control algorithm 15a for the respective terminal devices such as a fuel injection valve 17, a fuel pump 18 and an ignition control unit 20 connected to the signal port selected by the I/O control algorithm 15b, thereby to enable the start and running of the vehicle.
If the reference ID code stored in the EEPROM 13A and the key ID code transmitted from the key 2 and read in do not match each other or they are not in a predetermined relationship, the compare function unit 13S does not issue an enable signal. Accordingly, the start of the vehicle by the ECU 16 is inhibited, and a horn 14 is activated by the immobilizer CPU 13 to provide an appropriate alarm and display.
When the enable signal transmitted from the compare unit 13S is not correct data, the start of the vehicle by the engine ECU 16 is also inhibited. Thus, the illegal start-up of the engine and the driving of the vehicle by a wrong key are prevented to ensure the vehicle anti-theft function.
Although the immobilizer unit 10 and the engine ECU 16 are separate from each other in the system of FIG. 8, the function of the immobilizer unit 10 and that of the engine ECU 16 may be integrated into one unit as an Integral-type ECU 30a with an anti-theft function, as shown in FIG. 9, whereby the number of parts is reduced to increase the productivity and reliability. Since, in such integral structure, it is not necessary to encode the signal transferred from the immobilizer CPU 13 to the engine ECU 16, a simple binary signal can be utilized as an enable signal.
The function of the above described transponder type immobilizer for preventing illegal engine start-up and vehicle driving is very effective for vehicles to be used in areas or countries where thefts occur frequently, but, if such a function is provided even on vehicles to be used in areas where thefts occur infrequently, users are undesirably forced to share the cost burden of the unnecessary equipment. Accordingly, it is preferable that vehicles which are or are not equipped with the anti-theft function are manufactured in parallel depending on their destination.
FIG. 10 shows the construction of the main portions of an ECU 30b without the anti-theft function, which is to be mounted on vehicle which is not to be equipped with the anti-theft function, instead of the ECU 30a with the anti-theft function.
As apparent from the comparison of FIG. 10 with FIGS. 8 and 9, the transmitter 4 of the key 2 and the induction coil 6 of the key cylinder 5 have been removed, and in the ECU 30b, the anti-theft unit elements such as the I/F circuits 11 and 12 and the immobilizer CPU 13 which are included in the immobilizer unit 10 of FIG. 8 have been removed. As for the ROM for storing the engine control program executed by the engine ECU 16, the above ROM 15 in FIG. 8 including the anti-theft algorithm 15c for performing the verification of the enable code, or the like has been replaced with ROM 15' which does not include anti-theft algorithm 15c.
Generally, the ECUs 30a and 30b are connected to the terminal devices such as the antenna unit 29, the fuel injection valve 17, and the like by the connectors 40 and 50 which are relatively easily inserted and removed. Accordingly, there was a problem that, once an ill-intentioned third party illegally gets an ECU 30b having no anti-theft function and replaces an ECU 30a with the ECU 30b, the starting and driving of the vehicle would be possible without the discrimination of ID code outputted from the antenna unit 29, and thus the theft of the vehicle would be accomplished.
In addition, the ROM 15 (15') is also connected to the CPU within the engine ECU 16 by an IC socket which is inserted or removed with relative ease. Accordingly, there was a similar problem that, once an ill-intentioned third party illegally replaces a ROM 15 which includes the anti-theft algorithm with a ROM 15' which does not include the anti-theft algorithm 15c, then the starting and driving of the vehicle would be possible without the discrimination of the enable code outputted from the immobilizer CPU 13 in the engine ECU 16, and thus the theft of the vehicle would be accomplished.